Well for starters, you should atleast be able to tip-toe your feet off the ground while sitting on the bike, that helps if your get into a hairy situation and you need to plant your feet on the ground to straighten yourself out. The 250 2 strokes have explosive powerbands, so you should atleast be 155 pounds or more to keep the front end off the ground, but again, ive seen 11 year olds ride 250`s, its all about personal riding experience. Have you ever owned a dirtbike? Just some things to consider.